Been sloping...

[Phil_G]

Just me on me todd at Baildon today, Billy no-mates, everybody cried off which was a shame cos the weather was brilliant,
sunshine all day and a 12-15 westerly Fish and chips for one please
I'm joshing, it was good, sometimes quiet is nice, & there were several dog walkers to chat to & dogs to fuss
Didnt get there till 2pm as I'd forgotten Saturday traffic was heavy.
Took my older Remcom Impala for an airing and the Lidl Wing, flew them back to back all day. Bliss
I was using Shauns Digit Midget tranny as I'd been updating his NRF stuff, its been a while since I flew a propo Impala,
it really is a brilliant model for relaxing on top of a hill. More aerobatic than you'd imagine too. Theres no video but
Shaun's seen the reeds Impala flying inverted (silver fus, red wings), but its so much easier on propo
I had to make a new hatch for it, in earlier photos you'll see it was black, but it was lost years ago complete with battery pack whilst
inverted, the hatch & battery are probably still on Callow Bank somewhere...
Thought maybe a couple of local flyers might turn up but no, left about 5:30 as visibility was getting very silhouetty

[chefsolaire]

Has your impala got a lifting tail or flat plate ?

[Phil_G]

I've several - all clark-Y tailplanes as designed

[Shaun]

Phil Smith knew his onions when it came to designing models and whether to use flat plate or lifting tailplanes.
I remember him explaining the theory to me many years ago when I asked him the same question re my Impala (that needed a new tailplane).

Shaun.

[PaulJ]

Phil Smith knew his onions when it came to designing models and whether to use flat plate or lifting tailplanes.
I remember him explaining the theory to me many years ago when I asked him the same question re my Impala (that needed a new tailplane).

Shaun.

So what was Phil Smith's theory?

A conventionally stable aircraft with the CG in front of the centre of lift, has a download on the tailplane, so I have always thought that a lifting section on the tailplane was acting in opposition to what it was trying to achieve. Most (if not all) light aircraft have a symmetrical section on the tailplane and many (if not all) airliners have an inverted aerofoil on the tail (though this may also be related to it's function as the aircraft approaches Mach1).

Paul

[Shaun]

When I said I remember him explaining, I meant the conversation not the theory Paul, it was over 40 years ago but I know what I've been doing wrong with my Graupner Amigo. The tailplane needs inverting so it will be stable when thermalling at Mach 1.

Cheers,

Shaun
.

[Mike_K]

The green and yellow Impala I flew at Ivinghoe has a flat plate stabiliser and it flies as well (and the same) as the original, so I'm not certain the theories match with reality. It originally did need some elevator trim, so the incidence was altered, I can't remember if it needed up or down though, it's been like that since the 1990s.

[chefsolaire]

The reason I ask is that I used to fly my Wizard of Oz with the lifting tail plane as on the plan – and found it far harder to stop zooming than the zeitgeist which has a flat plate. I put it down to a longer tail moment on the zeitgeist

It was somebody on this forum who suggested changing the tailplane to a flat plate and it’s been much better since

I seem to remember that the reason for lifting tailplane in free flight models is that it stops the Zoom – as the plane moves faster the tail plane lifts and so brings the nose down


Not quite sure I get that - surely the speed picks up in a dive rather than in the ensuing Zoom where speed is bled off.

The Wizard of Oz with its lifting tailplane had the C of G further back than you would expect – as in many free flight planes, I think. Free flight planes often have a larger tailplane which makes you think it’s starting to fly like a tandem wing glider which explains the C of G

Anyway, for what it’s worth, I think the Wizard of Oz flies better with a symmetrical tailplane

[chefsolaire]

The last time I got in through the back stairs on a easyJet flight, it struck me that the tailplane was an inverted lifting section

Too much thinking is probably bad for you…

[Martin]

Large area, lifting tailplanes are normally inefficient compared to just making the main wing a bit bigger, and moving the c.g. forward so the tailplane doesn't need to provide any lift. A larger lifting surface is always more efficient than a smaller one.
Some competition classes may only limit the main wing area, rather than the total horizontal area, and then a large lifting tailplane might be useful in slow- flying, lightly loaded duration events - it's a way of getting extra lifting area, and therefore reducing the overall wing loading and sinking speed.

In free flight events, there may be advantages in getting the model to transition smoothly from a high speed, near vertical climb into a slow circling glide.

For radio control, I've always found a flat plate tailplane, or a symmetrical section, works best.